Recently, a variety of webs such as films or nonwoven fabrics are manufactured and used for various purposes. Defects in said webs, such as a tear (a portion at which fibers are broken) or a portion having insufficient strength, have occurred during the manufacturing process or the conveying process. To provide high quality products, it is necessary to detect such defects and remove same.
Conventionally, regarding the detection of defects in a film, there are devices for detecting defects in a film, in which light from a light emitter is irradiated on a surface of the film, and the amount of light passing through the film is measured with a detector arranged on the back side of the film. However, in conventional detecting devices, it is possible to accurately detect defects when said defects of the film exist in a relatively broad area, but it is difficult to accurately detect defects when defects of the film exist in a relatively narrow area. Also, since conventional detecting devices includes a complex means for the determination of defects, conventional detecting devices are expensive and the operation thereof is complex.
Moreover, conventionally, there are no devices for rapidly and reliably detecting defects such as tears in a web having network structures, such as nonwoven fabrics or the like. Therefore, it is necessary that the detection of defects such as tears in a web having network structures, such as nonwoven fabrics or the like, must be done by visual inspection by operators. It is therefore necessary to increase the number of operators, resulting in an increase in manpower in a manufacturing process. Also, visual inspection of defects in a high speed continuous manufacturing process results in the operators becoming fatigued thereby making it difficult to carry out a continuously accurate inspection of defects during the manufacturing process, and accordingly, the inspection of defects is carried out slowly by having to rewind the web after manufacturing the web. Therefore, an inspection of defects is not only laborious, but is also apt to result in a delay in the feedback of defect occurrence during manufacturing. Also, as it is difficult for the operators to maintain constant vigilance over a long time period of time, defects are sometimes overlooked.